1. Field of the Invention
The present invention relates to a semiconductor optical device.
2. Related Background of the Invention
One type of conventional semiconductor optical devices includes an active layer having a bulk structure, and the active layer is provided between the upper cladding layer and the lower cladding layer. This type encompasses semiconductor optical amplifiers, and in order to reduce the dependence of amplification characteristics thereof on polarization direction, the semiconductor optical amplifier includes a mesa-shaped active layer and the cross section of the active layer, taken along a plane intersecting with the light guiding direction in which light in the active layer propagates, is square. Publication (T. Ito et al. OECC' 97, PDP101, pp 2-3, 1997) discloses such a semiconductor optical amplifier.